This invention relates to the method of manufacturing heating furnace parts and, more particularly, to the method of manufacturing parts, for example, a process tube, constituting a diffusion furnace which is employed at the diffusion step in the cause of manufacturing a semiconductor device.
To date, high purity quartz glass has been exclusively used as the material of the parts of a diffusion furnace for the manufacture of a semiconductor device, for example, the material of a process tube. In recent years, however, not only quart glass but also silicon carbide is widely accepted for this purpose. The silicon carbide has not only great thermal shock resistance but also great mechanical strength during the thermal cycle of high temperature heating and cooling applied in the diffusion of an impurity into a semiconductor substrate. Therefore, the silicon carbide has been regarded as excellent material for a process tube of a diffusion furnace. However, the conventional process tube prepared from silicon carbide has failed to have sufficiently high purity.
The silicon carbide process tube of the diffusion furnace is generally manufactured through the steps of acid treatment of raw silicon carbide powder, molding the acid treated silicon carbide powder, purification of the molded product, impregnation of high purity silicon, and final acid treatment. However, even such a purification process has failed to completely remove the fine remnants of harmful impurities in the product, exerting noticeably adverse effects on the performance of a manufactured semiconductor device. Particularly, the adverse impurities trapped in the raw silicon carbide particles present extreme difficulties in the subsequent removing step. Such harmful impurities are released from the raw silicon carbide particles during the aforementioned diffusion step at a high temperature, supposedly contaminating the quality of a finished semiconductor device.